The invention relates to an apparatus for measuring the mass of a flowing medium, and, in particular, to an apparatus for measuring the aspirated air mass in an internal combustion engine. The apparatus includes a flow conduit for the medium which has a restricted section, and a bypass line which has a mouth connected to the restricted section of the flow conduit, through which a mass of the medium flows which is at a predetermined proportion with respect to a mass of the medium flowing through the flow conduit and discharges into the restricted section of the flow conduit. In this apparatus, the temperature and/or resistance of at least one temperature-dependent resistor disposed within the bypass line is regulated in accordance with the flowing mass of medium, wherein the control variable of the temperature-dependent resistor is a standard for the flowing mass of medium.
Such an apparatus for measuring the mass of a flowing medium is already known; however, when this known apparatus is used for measuring the mass of air aspirated by an internal combustion engine, the pulsations in the aspirated air, which are particularly pronounced in certain operating ranges, cause a falsification of the measurement signal. This is particularly caused by the fact that in a restricted section, such as a Venturi or a nozzle in the air intake tube of the engine, the pressure drop is greater with a pulsating flow than with a flow which is free of pulsation. Since the mass of air flowing through the bypass line is dependent on the pressure drop in the restricted section, measurement errors result from the pressure drop dependent upon the pulsation, since the signal generated by the air meter is not only a function of the aspirated air mass but also a function of the amplitude of the pulsation.